1. Field of the Invention
The present invention relates to an epoxy resin-based composite material which can be widely used in, for example, an artificial satellite body structure, an aircraft body structure, a radar dome body structure, and an antenna body structure as well as a golf club shaft, a tennis racket, a fishing rod, and an electric appliance.
2. Description of the Related Art
A material which is light, has a high rigidity and exhibits a high mechanical strength is required as a structural material in the fields of an artificial satellite, an aircraft, etc. It was customary in the past to use as such materials CFRP containing a carbon fiber as a reinforcing material, or reinforcement and a composite material including an epoxy resin as a matrix and a reinforcement such as a boron fiber, a silicon carbide fiber, or a glass fiber. These epoxy resin-based composite materials are excellent in mechanical properties, electrical properties, water resistance, heat resistance and chemical resistance.
The epoxy resin, which is thermosetting, is used in the epoxy resin-based composite material as a matrix in the form of a composition prepared by adding a curing agent, a curing catalyst, etc. to the thermosetting epoxy resin. However, in the conventional epoxy resin-based composite material containing the epoxy resin composition, the properties of the composite material are markedly varied by the curing agent and the curing catalyst contained in the matrix material, making it difficult to select appropriately the curing agent and the curing catalyst. In addition, how to perform the curing operation is an important technical problem to be solved. What should also be noted is that the thermal curing reaction is carried out at high temperatures, with the result that it is also important to take suitable measures for saving the required energy and for improving the operating environment.
For example, boron trifluoride complex or dicyandiamide is used as a curing agent for a thermosetting epoxy resin. However, a composite material formed by using an epoxy resin composition containing boron trifluoride as a curing agent is markedly poor in its corrosion resistance and electrical properties. It follows that the use of boron trifluoride as a curing agent is much restricted. On the other hand, the dicyandiamide curing agent is poor in compatibility with an epoxy resin, making it very difficult to disperse the curing agent uniformly in the epoxy resin composition.
It is also proposed to employ a laminate structure in various composite materials including an epoxy resin-based composite material. Specifically, it is proposed that a reinforcement comprising a fibrous sheet formed by arranging carbon fibers or boron fibers in one direction and a resin composition acting as a matrix are combined and, then, a plurality of the sheets are laminated, followed by curing the matrix so as to form a composite material exhibiting a high mechanical strength and a high elasticity. However, the composite material of this type gives rise to serious problems in terms of, for example, the impact resistance, crack resistance and mechanical strength in directions other than the arranging direction of the fibers of the sheet-like reinforcement.